Relationship between camera aperture and depth of field

"Aperture", which is a device used to control the amount of light entering the photosensitive surface of the fuselage through the lens, is usually located inside the lens. We use the f value to represent the aperture size.

Aperture f value = lens focal length/lens aperture diameter

As can be seen from the above formula, to achieve the same aperture f value, the aperture of a long focal length lens is larger than that of a short focal length lens. The complete series of aperture values is as follows:

f 1？ /? f 1.4？ /? f2？ /? f2.8？ /? f4？ /? f5.6？ /? f8？ /? f 1 1？ /? f 16？ /? f22？ /? f32？ /? f44？ /? f64

The above aperture values are commonly used in our general camera lenses, and the smaller the number (? For example, f 1.4), the larger the light input, the larger the relative aperture number (for example, f22), but the smaller the light input. So when we talk about large aperture, we usually mean smaller aperture value, which beginners often confuse. ?

There is a "one grid" (or "one level") difference in light quantity between each group of adjacent aperture values. For example, f 1.4? It is one grid away from f2 and one grid away from f5.6 and f8. The amount of light entering each aperture is multiplied. For example, the amount of light entering f4 is twice that of f5.6, and that of f2.8 is twice that of f4. In this way, the amount of light entering f2.8 is four times that of F5.6 .. In fact, it doesn't matter if it doesn't count. At present, all you need to know is that the light difference of each aperture is double, and the other thing is to take some time to write down the aperture value above. ?

It is worth mentioning here that the smaller the f value of the aperture, the more light enters in the same unit time, and the light entering amount of the upper level is exactly twice that of the lower level. For example, if the aperture is adjusted from f8 to f5.6, the amount of light entering will double. We also said that the aperture should be opened one level. For consumer digital cameras, the aperture f value is often between f2.8? -? F 16. In addition, many digital cameras can adjust the aperture with13.

Next, "depth of field" refers to the distance range that is completely clear (that is, not blurred) on the negative after focusing. The depth of field is closely related to the length of lens focal length, the size of aperture and the distance of photography. Usually, the longer the focal length of a lens (such as a long lens), the larger the aperture, the closer the shooting distance and the shallower the depth of field; The shorter the focal length of a lens (such as a wide-angle lens), the smaller the aperture, and the farther the camera is, the deeper the depth of field will be? .

Every lens with different focal length and aperture size will have different depth of field changes. Most manual lenses are often engraved with Jing Shenbiao for users to judge, while most autofocus lenses use simplified Jing Shenbiao. In our elementary course, we won't teach you how to watch Jing Shenbiao. On the one hand, it is boring to learn, on the other hand, ordinary photographers really seldom check this function. ?

Because the depth of field is very important for a photo, in this course, we will experience the change of depth of field when using different apertures and lenses. It will be easier to take pictures in the future after you are familiar with the performance of the depth of field changes of your usual lenses. ?

First of all, you need a model to cooperate with you (just find your friends and relatives, don't be picky about beauty and ugliness, we are doing an aperture depth of field practice class now, not taking pictures), and then find a venue with a changing background (such as a park) to connect the camera to cable release and put it on a tripod. Because when we shoot with a small aperture later, the shutter speed may be very slow, and if we don't shoot with a tripod, we may get a shaking picture. ?

Next, prepare a pen and paper for recording. First install your usual lens, check the range of lens aperture value from maximum to minimum, and then record it. Take our lens as an example, starting with the maximum aperture f2.8, then f4, f5.6, f8, f 1 1, f 16. ?

After asking the model to locate, we started taking pictures. People who use automatic cameras can switch their cameras to "aperture priority" mode. At first, we start with the maximum aperture, and then adjust the aperture in turn until we shoot the minimum aperture. Don't forget to write down the aperture value you used when shooting. People who use an automatic camera can give it to the camera for metering, just change the aperture in sequence. People who use manual cameras (such as FM2) must change the appropriate shutter value to match each aperture. Anyway, just adjust the aperture first and then find a shutter that can expose ok. For those who don't know how to use the "Aperture Prerequisite" or can't make correct exposure, please read the instruction manual of your camera, which will teach you how to operate it. ?

In fact, in a word, large aperture and long focal length are often suitable for portraits and still life shooting, which can cause shallow depth of field effect, that is, the effect of clear theme and blurred background. Generally speaking, fashion machines are not easy to make, but the focal length is slightly longer, such as DC with a focal length of 10X.

Application of aperture

Aperture is one of the most important photographic elements in photographic creation. In addition to controlling the input of light to meet the needs of exposure, it is also an important means to obtain specific artistic effects.

1, the unity of opposites between large aperture and imaging quality. Generally speaking, the imaging quality is relatively poor at large aperture, but the imaging quality of the new generation lens has been greatly improved at the maximum aperture. By making full use of the imaging characteristics of large aperture, unique images can be obtained. Because the depth of field is small at this time, it is convenient to clearly reflect a specific area and highlight the main body when other parts are relatively blurred.

When the light is poor, such as shooting with a hand-held camera, you can use a high-speed shutter with a large aperture to prevent the vibration of the machine from affecting the imaging clarity. Some photographers rarely use the maximum aperture, and usually only use f5.6 and f4. In order to give full play to the characteristics of the maximum aperture, they should dare to use the maximum aperture. For example, the aperture of a large aperture standard lens can completely use the maximum aperture such as f 1.8, f 1.4, while the aperture of a medium telephoto lens should dare to use the maximum aperture f2.8 at this time, combined with the camera distance and the distance between the background and the subject (the farther the background is from the subject, the picture quality of the maximum aperture may not be as good as that of the medium aperture, but the loss in this respect is still worthwhile compared with the artistic effect obtained.

2. Blur the background. When blurring the background, you usually choose a large aperture or a telephoto lens. How big is the aperture? In fact, except for telephoto lenses with a focal length of 200mm or even longer, the maximum aperture is generally used. When shooting with a standard lens, you may choose the maximum aperture f2.8 or even f 1.4. Only in this way can you get a unique charm and really separate the subject from the background. Because the depth of field of digital cameras is relatively large, it is difficult to highlight the subject without using the maximum aperture.

3. Small aperture and long depth of field. Small aperture is often used to obtain large depth of field when shooting scenery films, but factors such as lens focal length and shooting distance must be combined. If you use a telephoto lens, even if you use f32 aperture, you won't have much depth of field at a distance of 2-3 meters. In other words, as long as the subject and background are at infinity, there will be a great depth of field even if the aperture is large.

4. The aperture size varies according to the theme. In figure photography, large aperture is often used, while landscape photography has more opportunities to use small aperture. To shoot a stream, it takes 1/8- 1/2 seconds to show the movement of the running water. Not using a small aperture will inevitably lead to overexposure; If you shoot the shadow of a wave ship under the backlight, if you use small apertures such as f22 and f32, the tiny wave light on the water surface will have the effect of adding a starlight mirror; When shooting fireworks and other subjects, because it takes 1/2s- 1s exposure time to perfectly present the shape of fireworks, it is also necessary to choose a small aperture.

5, small aperture should be used with a tripod. Shooting still life scenery and other subjects with small aperture requires high imaging clarity. F22 aperture is used for medium illumination, and the shutter speed is often around 1/30 seconds. In the absence of a tripod, camera shooting by hand often affects the clarity because of machine vibration, human physiological movement and other factors. Therefore, in the case of low illumination, use a small aperture and make full use of various brackets to support the camera reasonably. If you use a digital camera, you can improve the sensitivity to make up for it.